The present invention relates to an image forming method using a toner composed of flattened spheroid particles (hereinafter referred to simply as flattened toner) as a toner of a two-component developer or a single-component developer for use in a copying machine, a printer, etc.
An image which is formed by using a toner produced by a usual pulverization method or polymerization method does not become a good glossy image owing to ruggedness produced on the surface resulted from the large amount of toner consumed; therefore, it has been difficult to obtain a high-quality image. Further, in the transfer process, the toner layer becomes thick because of the large amount of toner consumption to make the transfer ratio low; therefore, it has been impossible to obtain a high-density image, and occurrence of toner scattering has been making it impossible to obtain a good image.
Up to now, in order to obtain a printing-like, high-quality image, it has been made the attempt that the amount of toner consumption is made small by making the particle diameter of the toner smaller, to eliminate the ruggedness on the image surface to obtain a uniform gloss; however, because the covering power of the toner was lowered with the particle diameter of the toner being made smaller, a sufficient image density has not been able to be obtained, and because image forming processes such as development, transfer, and cleaning of the photoreceptor became difficult, a high-quality image has not been obtained by an image forming method based on electrophotography. Further, if toner particles having such a small particle diameter as 2 to 3 xcexcm are used, in the case where an operator inhale the toner particles, there is a risk that he suffers from a disease such as pneumoconiosis; therefore, it is not preferable from the view point of safety and sanitation.
When a color image (having a printed area ratio of 25%) is formed by superposing color toner images by an electrophotographic method using spherical-shaped or indefinite-shaped color toners having a particle diameter of about 5 xcexcm, which does not cause pneumoconiosis etc., the amount of toner consumption is about 90 mg per print sheet of A-4 size, and a thick toner layer is to be processed in development, transfer, and fixing. For this reason, scattered toner particles are observed in the toner image, and ruggedness is produced on the image surface, to make the difference in gloss between a toner deposition area and the background area; that is, it is the present state of the art that an image having a high image quality cannot be formed.
Further, the present invention relates to an image forming apparatus comprising a fixing device for use in a copying machine, a printer, a FAX machine, etc., and in particular, to an image forming apparatus capable of making fixing performance better by using a flattened toner in the developer.
Because an image formed by an image forming apparatus which forms a toner image on an image forming member using a toner composed of spherical-shaped or indefinite-shaped particles produced by a usual pulverization method or polymerization method, and then transfers the toner image onto a transfer material, to fix it, by an image forming apparatus which superposes toner images on an image forming member to form a color toner image composed of the toner images superposed on the image forming member, and then transfers the toner images all at a time, to fix them, by an image forming apparatus which transfers sequentially onto an intermediate transfer member toner images which have been formed on an image forming member in each of image forming units using a toner having a varied color for each, to form a color toner image composed of the toner images superposed on the intermediate transfer member, and then transfers the toner images on the intermediate transfer member all at a time, to fix them, or by the like, produces ruggedness on the image surface owing to the large amount of toner consumption, it has been difficult to obtain a printing-like image quality. Further, because of a large amount of toner consumption, toner layer became thick to make the transfer ratio low; therefore, a high-density image could not be obtained, and toner scattering occurred to make it impossible to obtain a good image. Especially, this problem became remarkable in the case of a color toner image composed of toner images superposed, and also fixing performance was bad.
In order to solve the above-mentioned problems, the inventors of this application has been attempting to make a toner layer thinner and flat, and in particular, to make a layer of superposed color toners thinner and flat; however, owing to the disturbance of the flattened toner particles in fixing (disturbance of the toner image), if a toner image is fixed under high pressure (Especially for a color toner image composed of toner images superposed, because it has a thick toner layer, the toner disturbance is remarkable, and higher pressure is necessary.), it is posed a problem that toner particles are crushed and spread to produce a disturbance of image, and because it is necessary to broaden the width of the nip portion owing to the spread of toner particle crushing (for a color toner image composed of toner images superposed, it is necessary to make the width of the nip portion broader owing to the layer thickness being made thicker), also it is posed a problem that warm-up time becomes longer.
The present invention has been proposed in view of the above-mentioned points of problem, and it is its object to provide an image forming method using a toner composed of flattened particles to be used with a carrier in a two-component developer or as a single component developer to make it possible to obtain a high-density image even with a small amount of toner consumption and to make it possible to obtain a high-quality image with little ruggedness and without toner scattering.
(1) It is the first object of the present invention to provide an image forming method in which flattened toner particles are deposited on an image forming member or a transfer member in such a way that the toner layer may be made thinner by taking into account the posture of the toner particles being deposited, and development, transfer, and fixing are performed satisfactorily.
(2) The second object of the present invention is to provide an image forming method in which, as a result of it that attention is paid to it that, by using an external additive of the flattened toner, the state of charge distribution on the flattened toner particles is improved to give a proper amount of fluidity, an external additive having a proper charging property is added to the toner, to make development, transfer, and fixing performed satisfactorily.
(3) The third object of the present invention is to provide an image forming method in which, as a result of it that attention is paid to it that, in adding an external additive to a flattened toner, it is extremely effective to select suitably the relation between the size of toner particles and the particle diameter of the external additive, an external additive having a suitable particle diameter is added to make development, transfer, and fixing performed satisfactorily.
(4) The fourth object of the present invention is to provide an image forming method in which, as a result of it that attention is paid to it that if there is a dispersion not smaller than a certain limit in the size and shape of the flattened toner, a good image cannot be obtained, a flattened toner which has been subjected to a suitable treatment and sorting in the manufacturing process of the toner is used, to make it possible to obtain an image having a high image quality.
(5) The fifth object of the present invention is to provide an image forming method in which, as a result of it that attention is paid to it that if there is a dispersion in the flat shape of the flattened toner, a good image cannot be obtained, the dispersion in the flattening ratio is limited to a proper amount, to make it possible to obtain an image having a high image quality.
(6) The sixth object of the present invention is, by solving the above-mentioned point of problems, to provide an image forming apparatus comprising a fixing device which prevents the generation of toner disturbance at the time of fixing, and prevents the generation of image disturbance owing to the spread of toner particle crushing, while the shortening of warm-up time is enabled by making the width of the nip portion narrower.
The object of the present invention is accomplished by an image forming method comprising: developing an electrostatic latent image on an image forming body employing a developing agent to form a toner image; transferring the toner image formed on the image forming body onto a transfer material; and fixing the toner image on the transfer material by a fixing device, wherein flattened toner particles which satisfy the following conditions are used as the developing agent: r2/r1 is not less than 0.6 and not more than 1.0; d/r2 is not less than 0.1 and not more than 0.5; r2 is not less than 5 xcexcm and not more than 20 xcexcm; and r1 is not less than 5 xcexcm and not more than 20 xcexcm, wherein r1 represents an average length of a major axis of each of the flattened toner particles, r2 represents an average length of a minor axis of each of the flattened toner particles, and d represents an average thickness of each of the flattened toner particles.
The first object of the present invention is accomplished by, as a preferable structure, an image forming method for carrying out development of a latent image on an image forming member using a two-component developer composed of a toner and a carrier or a single-component developer, and transfer and fixing of the formed toner image to a transfer member, characterized in that said toner particles have a flattened shape, and the particles attach to the surface of the image forming member or the transfer member in such a way that the surface of the spheroid-shaped particle enlarged and flattened by crushing in the direction perpendicular to the surface to be flattened (hereinafter referred to simply as flattened portion of the particle) is in contact with the surface of said image forming member or transfer member.
The second object of the present invention is accomplished by, as a preferable structure, an image forming method for carrying out development for depositing toner particles on a latent image portion of an image forming member using a two-component developer composed of a flattened toner and a carrier or a single-component developer composed of a flattened toner, characterized in that development is done by the particles of said toner with an external additive attached, the charge quantity Qxe2x80x2 (xcexcC/g) of the toner particles with the external additive attached is related to the charge quantity Q (xcexcC/g) of the toner particles having no external additive attached by an inequality
|Qxe2x80x2| greater than |Q|, 
and the toner particles make the attachment to the surface of the image forming member or the transfer member with the flattened portion kept in contact with the surface.
The third object of the present invention is accomplished by, as a preferable structure, an image forming method for carrying out development for depositing toner particles on a latent image area of an image forming member using a two-component developer composed of a flattened toner and a carrier or a single-component developer composed of a flattened toner, characterized in that development is done by the particles of said toner with an external additive attached, said development being carried out in such a way that the flattened portion of the toner particle is attached to the surface of the image forming member, and the particle diameter p of the external additive is related to the diameter r of the flattened portion and the thickness d of the toner particle by an equation
xe2x80x83p/r=10xe2x88x921xe2x88x925xc3x9710xe2x88x923. 
The fourth object of the present invention is accomplished by, as a preferable structure, an image forming method for carrying out development, using a two-component developer composed of a flattened toner and a carrier or a single-component developer composed of a flattened toner, to make the flattened portion of the toner particles attach to a latent image area of an image forming member, characterized in that said toner is a flattened toner prepared by flattening processing of a spherical polymerization toner, and the particle diameter distribution of the spherical polymerization toner having a particle diameter do for use in the preparation of said flattened toner is such that not less than 80% of the particles fall within the range expressed by
xc2xd less than d0/d0(M) less than 2, 
where d0(M) denotes the average of the particle diameter distribution.
The fifth object of the present invention is accomplished by, as a preferable structure, an image forming method for carrying out development, using a two-component developer composed of a flattened toner and a carrier or a single-component developer composed of a flattened toner, to make the flattened portion of the toner particles attach to a latent image portion of an image forming member, characterized in that the distribution of the ratio of the thickness d of said flattened toner and the diameter r of the flattened portion (flattening ratio) is such that not less than 80% of the particles fall within the range
xc2xd less than (d/r)/(d/r)(M) less than 2, 
where (d/r)(M) denotes the average of the flattening ratio.
The above-mentioned sixth object is accomplished by, as a preferable structure, an image forming apparatus, which forms an electrostatic latent image on an image forming member, to form toner image on said image forming apparatus, and after that, transfers said toner image onto a transfer material, to fix said toner image on said transfer material by a fixing device, characterized in that a flattened toner is employed for said toner, and by means of said fixing device, an electric field to cause the particles of said flattened toner to be brought in a flattened state on the surface of said transfer material, while the particles of the flattened toner attached onto said transfer material in a flattened state where the flattened portion is in contact with the surface of the transfer material are fixed onto said transfer material under the application of pressure.
Further, the above-mentioned sixth object is accomplished by, as an another preferable structure, an image forming apparatus which forms an electrostatic latent image on an image forming member, to form a toner image by developing said electrostatic latent image with a developer including a toner, and after repeating the formation of said toner image to form a color toner image composed of said toner images superposed on said image forming member, transfers said toner images composing the color toner image on said image forming member onto a transfer material all at a time, to fix the color toner image on said transfer material by means of a fixing device, characterized in that a flattened toner is employed for said toner, and by means of said fixing device, an electric field to cause the flattened toner particles to be brought in a flattened state on the surface of said transfer material, while the particles of the superposed flattened toners attached on said transfer material in a flattened state where the flattened portion is in contact with the surface of the transfer material are fixed onto said transfer material under the application of pressure.
Further, the above-mentioned sixth object of the present invention is accomplished by, as a still another preferable structure, an image forming apparatus which forms an electrostatic latent image on an image forming member, to form a toner image by developing said electrostatic latent image with a developer including a toner, and having a plurality of image forming unit for forming said toner image on said image forming member arranged on an intermediate transfer member, sequentially transfers the toner images formed on said image forming members respectively by using respective toners having a varied color for each image forming unit to the intermediate transfer member, to form a color toner image composed of toner images superposed on said intermediate transfer member, and then transfers said toner images composing the color toner image on said intermediate transfer member onto a transfer material all at a time, to fix the color toner image on said transfer material by means of a fixing device, characterized in that a plurality of flattened toners are employed for said plurality of flattened toners respectively, and by means of a fixing device, an electric field to cause the particles of said flattened toners to be brought in a flattened state on the surface of said transfer material, while the particles of the superposed flattened toners attached onto said transfer material in a flattened state where the flattened portion is in contact with the surface of the transfer material are fixed onto said transfer material under the application of pressure.